Haematology in Critical Care

A Practical Handbook

Jecko Thachil, Quentin Hill

• Publisher: Wiley-Blackwell
• Year: 2014
• ISBN:
  9781118869161
• Edition: 1
• Topic: Medicine
• Subtopic: Nursing

Issues of thrombosis, bleeding, and transfusion are extremely common, and often complex, in critically ill patients.

Haematology in Critical Care: A Practical Handbook providesa dependable source of expert guidance on how to handle common haematological problems seen in the critical care setting, as well as the acute care of patients with a primary haematological disorder.

Full-time clinical haematologists, regularly attending on intensive care, the Editors begin with an approach to abnormal laboratory tests, following with a disease-orientated approach to topics such as coagulation and haematological malignancy. Other key topics include paediatric and neonatal care, transfusion, point of care testing and the emergency presentation of haematological disease.

This title brings together two of the most highly scientific specialties in clinical practice, delivering a practical approach to these problems, and guiding the clinician through the diagnosis and management of common scenarios encountered in the ICU.

Section 1
Approach to Abnormal Blood Tests

Chapter 1
Diagnostic Approach to Anaemia in Critical Care

Stephen F. Hawkins¹ and Quentin A. Hill²

¹ Department of Haematology, Royal Liverpool University Hospital, Liverpool, UK

² Department of Haematology, Leeds Teaching Hospitals NHS Trust, Leeds, UK

Anaemia was defined by the World Health Organization as a haemoglobin (Hb) concentration less than 120 g/L (Hb < 36%) in females and less than 130 g/L (Hb < 39%) in males, but the lower level of the reference range for Hb may vary between laboratories. It is common in critically ill patients, occurring in up to 80% of those in intensive care units (ICUs) [1] with 50–70% having a Hb less than 90 g/L during their admission. By reducing oxygen delivery to the tissues, this may be tolerated poorly in those with cardiorespiratory compromise. In critical care, anaemia is commonly due to multiple factors such as inflammation, blood loss, renal impairment and nutritional deficiencies [2, 3] (see Table 17.1), but it is important to consider treatable causes and identify when more detailed investigation is needed. The role of transfusional support is considered in Chapter 17.

Tissue hypoxia exerts physiological control of Hb by triggering the release of erythropoietin (EPO) by the kidneys, which stimulates bone marrow (BM) erythropoiesis. Hb will increase so long as there are no underlying BM disorders (e.g. myelodysplasia) and there are adequate supplies of iron, vitamin B12 and folic acid. When a rapid marrow response occurs (e.g. following haemorrhage or replacement of a deficient vitamin), reticulocytes (young erythrocytes) enter the blood in large numbers and can be identified on the blood film (polychromasia) or by an elevated reticulocyte count. The normal lifespan for erythrocytes is 120 days, before being removed by the reticuloendothelial system (predominantly in the spleen and liver), but their lifespan may be shortened by inflammation, haemorrhage or haemolysis.

Diagnostic approach to anaemia in critical care

In the history, note pre-existing co-morbidities including renal and cardiac impairment. Also note medications, diet and symptoms suggestive of blood loss. Examine for jaundice, lymphadenopathy or organomegaly.

• If there is a sudden unexpected drop in Hb, this may be a sampling error; consider repeating the full blood count (FBC).
• Is the anaemia acute or chronic? This may inform the diagnosis, likely tolerance of anaemia and treatment strategy. Only 10–15% of ICU patients have chronic anaemia prior to admission [4].
• Is the anaemia isolated or are there other cytopenias? Thrombocytopenia (Chapter 3) is also a common finding (~40% of ICU patients) and will therefore often coexist with anaemia in critically ill patients. Common causes of both include sepsis, organ failure and acute blood loss, but important differentials include disseminated intravascular coagulation (DIC) (Chapter 9) and thrombotic microangiopathies (TMAs) (Chapter 11). Review the clotting and blood film. Haemophagocytic lymphohistiocytosis (HLH) is an important cause of fever and cytopenias that can present with single or multiple organ failure (see succeeding text under extrinsic causes of extravascular haemolysis).
• Pancytopenia may be an artefact (i.e. dilution during sampling) or result from BM failure or infiltration, infection, HLH, hypersplenism, drugs, autoimmune disease or megaloblastic anaemia. If pancytopenia is present, examine for splenomegaly and request a blood film and haematinics. If the cause remains unclear, the advice of a haematologist should be sought as a BM examination may be required.

If the cause of an isolated anaemia remains unclear, it is worth classifying on the basis of the mean cell volume (MCV) as this helps to direct further investigation (Figure 1.1).

Figure 1.1 Investigation of anaemia in critical care. MCV, mean cell volume; DIC, disseminated intravascular coagulation; TMAs, thrombotic microangiopathies; HLH, haemophagocytic lymphohistiocytosis; BM, bone marrow; AoCD, anaemia of chronic disease; PNH, paroxysmal nocturnal haemoglobinuria.

Normocytic anaemia (MCV within the normal range)

Anaemia is most commonly normocytic in critically ill patients and usually multifactorial [4]. Iatrogenic reasons include frequent blood sampling and haemodilution (intravenous fluid administration). Occult blood loss can occur as a result of gastrointestinal mucosal inflammation and contributed to by coagulation defects, thrombocytopenia and uraemia. Another important reason is secondary anaemia, also termed anaemia of chronic disease (AoCD) or anaemia of inflammation. This is the most common cause of anaemia in hospitalized patients and can be caused by infection, cancer, autoimmune disease or chronic kidney disease [5]. This results in a functional iron deficiency, whereby adequate iron stores are present but the availability of iron for erythropoiesis is reduced. Hepcidin, a peptide produced by the liver in response to inflammatory cytokines, may be at least in part responsible for this phenomenon. Typically, ferritin is elevated and serum iron and transferrin saturation are low. Iron supplementation usually produces no improvement (in contrast to true iron deficiency). In addition to functional iron deficiency, inflammation results in reduced EPO production, reduced marrow sensitivity to EPO and shortened red cell survival.

Check haematinics as combined deficiencies can result in a normal MCV. Additionally, due to the acute phase response, a normal ferritin does not exclude iron deficiency. Consideration should be given to the possibility of occult or recent bleeding. The anaemia is likely to resolve with improvement of the underlying conditions. Meanwhile, supportive management (including transfusion when required; see Chapter 17) is the mainstay of therapy, and blood sampling should be kept to a minimum.

Microcytic anaemia (MCV below the normal range)

This is often a result of iron deficiency (blood loss, malabsorption or dietary deficiency). It can also occur during prolonged and severe illness as an extreme form of AoCD. Less commonly, microcytosis can be due to a haemoglobinopathy (e.g. thalassaemia trait), acaeruloplasminaemia, myelodysplasia, hyperthyroidism, lead poisoning and some rare congenital conditions (e.g. congenital sideroblastic anaemia).

Iron deficiency can be associated with a thrombocytosis, especially with bleeding. Less frequently, severe iron deficiency may also result in a leukopenia and thrombocytopenia. The blood film may show hypochromic, microcytic red cells, polychromasia and pencil cell poikilocytes. The usual tests of iron status (ferritin and iron studies) are less likely to be informative in the c...

Table of contents

• Cover
• Title page
• Copyright page
• List of Contributors
• Preface
• Acknowledgements
• Section 1: Approach to Abnormal Blood Tests
• Section 2: Approach to Coagulation Problems
• Section 3: Approach to Transfusion Problems
• Section 4: Approach to Red Cell Problems
• Section 5: Approach to White Cell Problems
• Section 6: Admission to Intensive Care
• Section 7: Point-of-Care Testing
• Section 8: Haematology Drugs in Critical Care
• Section 9: Haematology in Paediatric and Neonatal Intensive Care
• Section 10: Haematological Emergencies
• Appendix A: Adult, Paediatric and Neonatal Haematology Reference Intervals
• Index
• End User License Agreement